You have to set the power on state through the tasmota web gui. Dr zzz’s has done a great you tube video on tasmota commands . I did mine through the tasmoadmin (formerly sonweb) addon which is also brilliant so that’s another option
I don’t think it’s anything in the mqtt commands unless you set retain state to true. There is something in the tasmota wiki page that explains why that’s not always a good idea.
I didn’t get on with understanding the command line commands very well. It didn’t seem to change the state hence discovering the tasmoadmin was a revelation. I suggest trying that instead it really is great